3A Low-Voltage Low-Dropout Regulator
LM39300/39301/39302
Minimum Load Current
The LM39300/1/2 regulator is specified between finite loads.
If the output current is too small, leakage currents dominate and the output voltage rises.
A 10mA minimum load current is necessary for proper regulation.
Transient Response and 3.3V to 2.5V Conversion
The LM39300/1/2 has excellent transient response to varia-tions in input voltage and load current. The device has
been designed to respond quickly to load current variations and input voltage variations. Large output capacitors are
not required to obtain this performance. A standard 47F output capacitor, preferably tantalum, is all that is required.
Larger values help to improve performance even further.By virtue of its low-dropout voltage, this device does not
saturate into dropout as readily as similar NPN-based de-signs. When converting from 3.3V to 2.5V, the NPN-based
regulators are already operating in dropout, with typical dropout requirements of 1.2V or greater. To convert down to
2.5V without operating in dropout, NPN-based regulators require an input voltage of 3.7V at the very least. The
LM39300/1/2 regulator will provide excellent performance with an input as low as 3.0V. This gives the PNP-based
regulators a distinct advantage over older, NPN-based linear regulators.
Error Flag
The LM39301 version features an error flag circuit which monitors the output voltage and signals an error condition
when the voltage drops 5% below the nominal output voltage. The error flag is an open-collector output that can sink
10mA during a fault condition.Low output voltage can be caused by a number of problems, including an overcurrent
fault (device in current limit) or low input voltage. The flag is inoperative during overtemperature shutdown.
Enable Input
The LM39301 version features an enable input for on/off control of the device. Its shutdown state draws “zero” current
(only microamperes of leakage). The enable input is TTL/ CMOS compatible for simple logic interface, but can be
connected to up to 20V. When enabled, it draws approxi-mately 15A.
Adjustable Regulator Design
The LM39302 allows programming the output voltage any-where between 1.25V and the 16V maximum operating
rating of the family. Two resistors are used. Resistors can be quite large, up to 1MΩ, because of the very high input
impedance and low bias current of the sense comparator: The resistor values are calculated by :
R1=R2(Vout/1.250-
1)
Where VO is the desired output voltage. Figure 1 shows component definition. Applications with widely varying load
currents may scale the resistors to draw the minimum load current required for proper operation (see below).
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